In recent years, a liquid crystal display device is often adopted as a display device for a monitor of a notebook-sized personal computer, a television receiver, or the like. The liquid crystal display device includes a liquid crystal display panel and a backlight unit that is disposed behind the liquid crystal display panel. In the liquid crystal display device, a transmittance (transmission amount) of light from the backlight unit is adjusted by the liquid crystal display panel, and a resulting image is formed on a front surface of the liquid crystal display panel.
As the backlight unit, there is increasingly used a type in which a plurality of LED lamps are arranged on a flat surface. The backlight unit includes a chassis that is an open box-shaped body, a substrate that is disposed at a bottom surface portion inside the chassis, a plurality of LED lamps that are mounted on the substrate, and a reflection sheet that is disposed inside the chassis so as to cover the substrate. The reflection sheet has a plurality of through holes, and the LED lamps penetrate through the through holes, respectively (see JP-A-2006-332024).
Most part of light from the LED lamps is used to directly irradiate the liquid crystal display panel on a front side, and remaining part of the light is reflected off the reflection sheet toward the liquid crystal display panel on the front side. The backlight unit irradiates an object to be irradiated (herein, the liquid crystal display panel) on the front side with planar light that is a combination of light emitted from the LED lamps and light emitted from the LED lamps and reflected off the reflection sheet.